/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.http.codec.json;

import java.lang.annotation.Annotation;
import java.lang.reflect.Type;
import java.nio.charset.StandardCharsets;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.Map;

import com.fasterxml.jackson.annotation.JsonView;
import com.fasterxml.jackson.databind.JavaType;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.type.TypeFactory;

import org.springframework.core.GenericTypeResolver;
import org.springframework.core.MethodParameter;
import org.springframework.core.ResolvableType;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.util.MimeType;
import org.springframework.util.ObjectUtils;

/**
 * Base class providing support methods for Jackson 2.9 encoding and decoding.
 *
 * @author Sebastien Deleuze
 * @author Rossen Stoyanchev
 * @since 5.0
 */
public abstract class Jackson2CodecSupport {

    /**
     * The key for the hint to specify a "JSON View" for encoding or decoding
     * with the value expected to be a {@link Class}.
     *
     * @see <a href="http://wiki.fasterxml.com/JacksonJsonViews">Jackson JSON Views</a>
     */
    public static final String JSON_VIEW_HINT = Jackson2CodecSupport.class.getName() + ".jsonView";

    private static final String JSON_VIEW_HINT_ERROR =
            "@JsonView only supported for write hints with exactly 1 class argument: ";

    private static final List<MimeType> DEFAULT_MIME_TYPES = Collections.unmodifiableList(
            Arrays.asList(
                    new MimeType("application", "json", StandardCharsets.UTF_8),
                    new MimeType("application", "*+json", StandardCharsets.UTF_8)));


    private final ObjectMapper objectMapper;

    private final List<MimeType> mimeTypes;


    /**
     * Constructor with a Jackson {@link ObjectMapper} to use.
     */
    protected Jackson2CodecSupport(ObjectMapper objectMapper, MimeType... mimeTypes) {
        Assert.notNull(objectMapper, "ObjectMapper must not be null");
        this.objectMapper = objectMapper;
        this.mimeTypes = !ObjectUtils.isEmpty(mimeTypes) ?
                Collections.unmodifiableList(Arrays.asList(mimeTypes)) : DEFAULT_MIME_TYPES;
    }


    public ObjectMapper getObjectMapper() {
        return this.objectMapper;
    }

    /**
     * Subclasses should expose this as "decodable" or "encodable" mime types.
     */
    protected List<MimeType> getMimeTypes() {
        return this.mimeTypes;
    }


    protected boolean supportsMimeType(@Nullable MimeType mimeType) {
        return (mimeType == null || this.mimeTypes.stream().anyMatch(m -> m.isCompatibleWith(mimeType)));
    }

    protected JavaType getJavaType(Type type, @Nullable Class<?> contextClass) {
        TypeFactory typeFactory = this.objectMapper.getTypeFactory();
        return typeFactory.constructType(GenericTypeResolver.resolveType(type, contextClass));
    }

    protected Map<String, Object> getHints(ResolvableType resolvableType) {
        MethodParameter param = getParameter(resolvableType);
        if (param != null) {
            JsonView annotation = getAnnotation(param, JsonView.class);
            if (annotation != null) {
                Class<?>[] classes = annotation.value();
                Assert.isTrue(classes.length == 1, JSON_VIEW_HINT_ERROR + param);
                return Collections.singletonMap(JSON_VIEW_HINT, classes[0]);
            }
        }
        return Collections.emptyMap();
    }

    @Nullable
    protected MethodParameter getParameter(ResolvableType type) {
        return type.getSource() instanceof MethodParameter ? (MethodParameter) type.getSource() : null;
    }

    @Nullable
    protected abstract <A extends Annotation> A getAnnotation(MethodParameter parameter, Class<A> annotType);

}
